Mass storage systems may generate a huge amount of control metadata. The control metadata is metadata that is generated by the storage system for managing the objects handled by the storage system, such as metadata that facilitates writing and reading data stored in the system, metadata about logical volumes or snapshots creation and deletion.
The control metadata may include for example, information about address mapping, volumes and snapshots information, journal (logs) about changes, etc.
Committed information is information that is updated as part of a request received from a host that is coupled to the storage system (or from another module of the storage system) and the request was responded with an acknowledgment assuring the handling of the request. Committed information should not be lost, even upon failover (i.e., when a primary control node fails, and the secondary control node takes control from the point of the failure).
A successful failover requires that the secondary control node will have an updated version of control metadata.
When the storage system is structured as a cluster of control nodes, the control metadata needs to be shared or communicated efficiently among the control nodes, to enable the successful failover, or at least to enable other nodes (nodes that did not created the metadata) to provide services that require access to the control metadata.